Modelling soil water and salt dynamics under pulsed and continuous surface drip irrigation of almond and implications of system design

Abstract

The HYDRUS-2D model was experimentally verified for water and salinity distribution during the profile establishment stage (33 days) of almond under pulsed and continuous drip irrigation. The model simulated values of water content obtained at different lateral distances (0, 20, 40, 60, 100 cm) from a dripper at 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140 and 160 cm soil depths at different times (5, 12, 19, 26 and 33 days of profile establishment) were compared with neutron probe measured values under both irrigation scenarios. The model closely predicted water content distribution at all distances, times and soil depths as RMSE values ranged between 0.017 and 0.049. The measured mean soil water salinity (ECsw) at 25 cm from the dripper at 30, 60, 90 and 150 cm soil depth also matched well with the predicted values. A correlation of 0.97 in pulsed and 0.98 in continuous drip systems with measured values indicated the model closely predicted total salts in the root zone. Thus, HYDRUS-2D successfully simulated the change in soil water content and soil water salinity in both the wetting pattern and in the flow domain. The initial mean ECsw below the dripper in pulsed (5.25 dSm -1 ) and continuous (6.07 dSm -1 ) irrigations decreased to 1.31 and 1.36 dSm -1 , respectively, showing a respective 75.1 and 77.6% decrease in the initial salinity. The power function [y = ax -b ] best described the mathematical relationship between salt removal from the soil profile as a function of irrigation time under both irrigation scenarios. Contrary to other studies, higher leaching fraction (6.4-43.1%) was recorded in pulsed than continuous (1.1-35.1%) irrigation with the same amount of applied water which was brought about by the variation in initial soil water content and time of irrigation application. It was pertinent to note that a small (0.012) increase in mean antecedent water content (h i ) brought about 8.25-9.06% increase in the leaching fraction during the profile establishment irrespective of the emitter geometry, discharge rate, and irrigation scenario. Under similar h i , water applied at a higher discharge rate (3.876 Lh -1 ) has resulted in slightly higher leaching fraction than at a low discharge rate (1.91 Lh -1 ) under pulsing only owing to the variation in time of irrigation application. The influence of pulsing on soil water content, salinity distribution, and drainage flux vanished completely when irrigation was applied daily on the basis of crop evapotranspiration (ETc) with a suitable leaching fraction. Therefore, antecedent soil water content and scheduling or duration of water application play a significant role in the design of drip irrigation systems for light textured soils. These factors are the major driving force to move water and solutes within the soil profile and may influence the off-site impacts such as drainage flux and pollution of the groundwater.

Evaluation of water movement and nitrate dynamics in a lysimeter planted with an orange tree

“…Similar results were obtained in scenarios with different irrigation quantities (50%, 75%, and 125% of normal irrigation). A negligible impact of pulsing on moisture distribution pattern and drainage has been reported in earlier studies for different dripper discharge rates and spacings (Skaggs et al, 2010;Phogat et al, 2012). This observation further confirms that pulsing has little impact on solute distribution in the soil under optimal irrigation applications as compared to continuous irrigation.…”

“…Additionally, since in the present study we dealt with a tree, for which the root distribution development over time is not as fast as observed for seasonal crops like cereals, the root development was considered relatively constant for the modelling purpose. Hence, a static root distribution and variable atmospheric conditions produced a good approximation of plant uptake, as has been revealed in a number of earlier studies that used HYDRUS for modelling purposes (Sansoulet et al, 2008;Phogat et al, 2012Phogat et al, , 2013Ramos et al, 2011Ramos et al, , 2012Tournebize et al, 2012) …”

“…Other studies have also reported good performance of this software for various soil, water, and crop conditions under pressurised irrigation systems (e.g., Assouline et al, 2006;Ajdary et al, 2007;Patel and Rajput, 2008;Phogat et al, 2012Phogat et al, , 2013Ramos et al, 2012).…”

“…HYDRUS 2D/3D (Šimůnek et al, 2008, 2011) has been used extensively for evaluating the effects of soil hydraulic properties, soil layering, dripper discharge rates, irrigation frequency and quality, timing of nutrient applications on wetting patterns and solute distribution (e.g., Cote et al, 2003;Gärdenäs et al, 2005;Assouline et al, 2006;Hanson et al, 2006;Ajdary et al, 2007;Patel and Rajput, 2008;Šimůnek and Hopmans, 2009;Phogat et al, 2009Phogat et al, , 2010Phogat et al, , 2012Phogat et al, , 2013Li and Liu, 2011;Ramos et al, 2012) because it has the capability to analyse water flow and nutrient transport in multiple spatial dimensions (Cote et al, 2003).…”

Evaluation of nitrogen balance in a direct-seeded-rice field experiment using Hydrus-1D

“…The solute transport parameters were considered using the following values: the molecular diffusion coefficients in free water (D w ) for NH 4 + -N and NO 3 − -N were 1.52 and 1.64 cm 2 day −1 , respectively, the molecular diffusion coefficient in air (D a ) for NH 3 was 18057.6 cm 2 day −1 , the longitudinal dispersivity (12 cm) was considered equal to one-tenth of the profile depth (Phogat et al, 2012), and the Henry's law constant (K H , at 25 • C) for NH 4 + -N was 2.95 × 10 −4 (Renard et al, 2004). The distribution coefficient (K d ) for NH 4 + and for different soil layers is listed in Table 3, based on values for this region reported by Chen and Chiang (1963).…”